Strength members, reinforcing members, or structural members made of metal and having a bent shape are used in automobiles and various types of machines and the like. These bent members need to have a high strength, a light weight, and a small size. This type of bent member has been manufactured by welding of press formed members, punching of a plate, forging, and the like. However, it is difficult to further reduce the weight and size of bent members manufactured by these manufacturing methods.
In recent years, the manufacture of this type of bent member by the so-called tube hydroforming technique has been actively studied (see Non-Patent Document 1, for example). As described on page 28 of Non-Patent Document 1, there are various challenges in the tube hydroforming technique, such as the development of materials for use in the method and increasing the degree of freedom of shapes which can be formed, and therefore further technological developments are necessary in the future.
In Patent Document 1, the present applicant disclosed a bending apparatus. FIG. 3 is an explanatory view schematically showing that bending apparatus 0.
As shown in FIG. 3, the bending apparatus 0 manufactures a bent member 8 which intermittently or continuously has a bent portion which is bent two-dimensionally or three-dimensionally and a quench hardened portion in its lengthwise direction and/or in the circumferential direction in a surface which intersects the lengthwise direction, with a high operating efficiency while maintaining an adequate bending accuracy. To this end, the bending apparatus 0 performs the following operations on a steel pipe 1 which is a blank (a material to be processed) and which is supported by a support means 2 so as to be movable in its axial direction while feeding the steel pipe 1 from an upstream side towards a downstream side using a feed device 3 such as a ball screw:
(a) rapidly heating a portion of the steel pipe 1 with a high frequency heating coil 5 located downstream of the support means 2 to a temperature range in which quench-hardening is possible,
(b) rapidly cooling the steel pipe 1 with a water cooling device 6 disposed downstream of the high frequency heating coil 5, and
(c) imparting a bending moment to the heated portion of the steel pipe 1 to perform bending by two-dimensionally or three-dimensionally varying the position of a movable roller die 4 having at least one set of roll pairs 4a which can support the steel pipe 1 while feeding it.
List of Prior Documents
Patent Document 1: WO 2006/093006
Non-Patent Document 1: Jidosha Gijustsu (Journal of Society of Automotive Engineers of Japan), Vol. 57, No. 6, 2003, pp. 23-28